[dpdk-dev] [PATCH 1/2] drivers/mempool: add stack mempool handler as driver

[Shreyansh Jain]

Hello Olivier,

On Wednesday 29 March 2017 01:48 PM, Olivier Matz wrote:
> On Tue, 28 Mar 2017 17:12:47 +0530, Shreyansh Jain <shreyansh.jain at nxp.com> wrote:
>> Hello Olivier,
>>
>> On Friday 24 March 2017 09:52 PM, Olivier Matz wrote:
>> [..]
>>
>>> I tried to pass the mempool autotest, and it issues a segfault.
>>> I think the libraries are missing in rte.app.mk, so no handler is
>>> registered.
>>
>> I have been trying to simulate the segfault that you are referring to
>> above. But, I think it should not be the case. If a mempool handler is
>> not registered (as librte_mempool_ring was not included in
>> mk/rte.app.mk, so, no "ring_mp_mc"), the caller would get error.
>>
>> The mempool_autotest is reporting:
>>
>> --->8--
>> RTE>>mempool_autotest
>> cannot allocate mp_nocache mempool
>> Test Failed
>> --->8--
>
> Here are the reproduction steps:
>
>
> git clone http://dpdk.org/git/dpdk
> cd dpdk/
> wget -O - http://dpdk.org/dev/patchwork/patch/21986/mbox | git am -
> wget -O - http://dpdk.org/dev/patchwork/patch/21985/mbox | git am -
> make config T=x86_64-native-linuxapp-gcc
> make -j32 test-build
> echo 128 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
> mkdir -p /mnt/huge
> mount -t hugetlbfs none /mnt/huge
> echo mempool_autotest | ./build/app/test --
> # segfault

Thanks for the steps. I was able to reproduce this.
Don't know why it didn't work earlier.
one more comment below...

>
> # replay with debug
> make -j32 test-build
> make -j32 EXTRA_CFLAGS="-O0 -g" test-build
> ulimit -c unlimited
> echo mempool_autotest | ./build/app/test --
> # segfault + core dump
> gdb -c core ./build/app/test
>
> (gdb) bt
> #1  0x000000000064dead in rte_mempool_ops_alloc (mp=0x7f8816abdb40)
>     at /root/dpdk/lib/librte_mempool/rte_mempool_ops.c:101
> #2  0x000000000064c1e7 in rte_mempool_populate_phys (mp=0x7f8816abdb40,
>     vaddr=0x7f880987a800 <error: Cannot access memory at address 0x7f880987a800>,
>     paddr=6958852096, len=26761152, free_cb=0x64c032 <rte_mempool_memchunk_mz_free>,
>     opaque=0x7f8822334d4c) at /root/dpdk/lib/librte_mempool/rte_mempool.c:359
> #3  0x000000000064c9db in rte_mempool_populate_default (mp=0x7f8816abdb40)
>     at /root/dpdk/lib/librte_mempool/rte_mempool.c:572

I think adding the code that you suggested is not the right place. The 
problem is not in rte_mempool_ops_alloc, where you had suggested the 
check for NULL.

The problem is in rte_mempool_create where return value for 
rte_mempool_set_ops_byname is not being checked.

When the libraries are not statically compiled in, 
rte_mempool_set_ops_byname is returning NULL, which rte_mempool_create 
doesn't handle and goes on to call rte_mempool_ops_alloc - eventually 
segfaulting.


> #4  0x000000000064d3d4 in rte_mempool_create (name=0x9b1ff0 "test_nocache", n=12671,
>     elt_size=2048, cache_size=0, private_data_size=0, mp_init=0x0, mp_init_arg=0x0,
>     obj_init=0x49f309 <my_obj_init>, obj_init_arg=0x0, socket_id=-1, flags=0)
>     at /root/dpdk/lib/librte_mempool/rte_mempool.c:895
> #5  0x00000000004a20ed in test_mempool () at /root/dpdk/test/test/test_mempool.c:519
> #6  0x0000000000435189 in cmd_autotest_parsed (parsed_result=0x7ffe55006420,
>     cl=0x7c87090, data=0x0) at /root/dpdk/test/test/commands.c:103
> #7  0x00000000006749df in cmdline_parse (cl=0x7c87090,
>     buf=0x7c870d8 "mempool_autotest\n")
>     at /root/dpdk/lib/librte_cmdline/cmdline_parse.c:359
> (gdb) up
> #1  0x000000000064dead in rte_mempool_ops_alloc (mp=0x7f8816abdb40)
>     at /root/dpdk/lib/librte_mempool/rte_mempool_ops.c:101
> 101             return ops->alloc(mp);
> (gdb) print ops
> $1 = (struct rte_mempool_ops *) 0x4e69c00 <rte_mempool_ops_table+64>
> (gdb) print *ops
> $2 = {name = '\000' <repeats 31 times>, alloc = 0x0, free = 0x0, enqueue = 0x0,
>   dequeue = 0x0, get_count = 0x0}
>
>
> Regards,
> Olivier
>
>
>>
>>>
>>> Adding the following code in lib/librte_mempool/rte_mempool_ops.c
>>> fixes the crash.
>>>
>>>         ops = rte_mempool_get_ops(mp->ops_index);
>>> +       if (ops == NULL || ops->alloc == NULL)
>>> +               return -ENOTSUP;
>>>         return ops->alloc(mp);

If you think above explanation suffices, I will push a patch for error 
handling in rte_mempool_create returned by rte_mempool_set_ops_byname 
rather than above change originally suggested by you.

>>
>> Can you tell me for which case did your code reach
>> rte_mempool_ops_alloc() and segfault?
>>
>> In my case, librte_mempool_ring and librte_mempool_stack are not added
>> to mk/rte.app.mk and it is static compilation.
>>
>>>
>>> Now that drivers are not linked to the mempool library, it can
>>> happen that there is no handler. Could you please add this patch in your
>>> patchset?
>>
>> Yes, once I can get this issue reproduced. Because I think there is one
>> more place similar code should go (rte_mempool_ops_getcount).
>> As per what I can see, this would only happen if rte_mempool_xmem_create
>> is called and then directly alloc is called. That is not happening for
>> mempool_autotest.
>>
>> -
>> Shreyansh
>>
>
>